Plant Communities of the Midwest - NatureServe

Ecological groups allow us to think at bigger scales and consider ecological factors that may not
be readily apparent at the association level. As Grimm (1983, 1984) demonstrated in his studies of the
prairie-forest border in Minnesota (Figure 8), ecological groups can extend our understanding of
vegetation pattern beyond site and disturbance factors to historical and climatic factors. By working at
the scale of “Midwestern Tallgrass Prairies” and “Midwestern Oak Woodlands” we can incorporate
ecological studies that occur over much larger spatial and temporal scales than do many association
studies, and thereby we gain a perspective on the dynamics of individual associations within those groups.
So, this approach allows us to address the variety of ecological processes and abiotic factors affecting
midwestern plant communities, from the moisture/substrate gradient and the prairie-forest
physiognomic/fire gradient to the interactions of both of these gradients with climate.
V. PLANT COMMUNITIES OF THE MIDWEST
At this time, there are 588 associations (including 21 of uncertain status) and 258 alliances in the
Midwest (Table 7). The total number of associations in various states of the Midwest ranged from 74 in
Kansas and Nebraska to 185 in Michigan. By comparison, in 1991, the number of types catalogued in
natural community classifications from state to state varied from 25 in North Dakota to 191 in Minnesota.
Thus, the USNVC has helped to standardize the scale of community type definition across the region.
The midwestern associations can also be aggregated by ecological groups. The number of units
by ecological group level is summarized in Table 8. The total number of ecological groups in the
Midwest at Level 4 is 152, ranging from 38 in Kansas to 63 in Illinois and Michigan. The complete list of
associations in order of Ecological Group is presented in Table 9. Descriptions of each association are
provided in the Appendix. A summary of the fields, as laid out in each association description, is
presented in Box 1, followed by an example description.
Given the qualitative but extensive nature of the work completed to date, it is difficult to estimate
the degree to which associations may be added or subtracted in the Midwest. All twelve states in the
Midwest have helped review the associations presented here, and every attempt has been made to include
only vegetation types that meet the association concept. Many associations, however, are described only
briefly, and further research is needed to understand these types.
There is an urgent need for more extensive, quantitative-based surveys of many of these types.
Some states, such as Nebraska and Minnesota, are engaged in detailed, plot-based surveys across the
entire state. In Wisconsin, the entire Plant Ecology Laboratory vegetation data set that was developed by
Curtis and his students has been computerized (Umbanhower 1990). Analysis of these data at the local or
state level will, in turn, assist with more rigorous definitions of the associations. Other states are
collecting data on a project-by-project basis. Ultimately, a national plots database, which allows analyses
to be conducted across jurisdictional lines, will provide the quantitative data that will augment and inform
the qualitative global descriptions provided here. A collaborative project to develop such a plots database
is now underway at the National Center for Ecological Analysis and Synthesis (Peet et al. 2000).
PLANT COMMUNITIES OF THE MIDWEST – 2001
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